Plate cylinders--see, for example, German Published Patent Application DE-AS No. 21 33 890 to which U.S. Pat. No. 3,772,991 corresponds--have been proposed in which the plate cylinder is flattened at the outer circumference in the region of attachment of the printing plate, the flattened surfaces forming engagement surfaces for the marginal regions of the printing plate. A cover can be placed over the flattened surface to prevent lifting off of the end portions of the printing plate from the engagement surfaces. A cylindrical clamping element is located in the center of the cover, positioned in parallel to the axis of the cylinder, and engaging the marginal regions of the printing plate. The outer circumference of the cover is recessed with respect to the outer circumference of the printing cylinder, when covered by the printing plate.
The arrangement, as described, is quite space-consuming, particularly due to the clamping element provided therein. If such a plate cylinder is used in a rotary printing machine, the strips which do not print, that is, where no plate is exposed, result in substantial wide margins, which leads to a loss in paper, that is, printed coverage on the paper web. The recessed outer surface of the cover results in shocks and vibration upon engagement of the plate cylinder with an associated cylinder against which it runs off. Such shocks may lead to danger of damage to bearer rings and bearings for the printing cylinders. If plate cylinders are used which are quite wide, and which may carry two or more plates adjacent each other, vibrations and oscillations in the cylinder can result which reduce the quality of the printed subject matter being obtained. This effect is particularly pronounced if the printing cylinder carries a plurality of printing plates in circumferential direction since, upon each revolution of the printing cylinder, the number of jolts or shocks is increased, tending to cause oscillations of the cylinder system.